Biodiesel (fatty acid methyl ester) derived from oleaginous microbes—microalgae, yeast, and bacteria—can effectively displace both petroleum diesel and biodiesel produced from plant oils, according to the findings of a new study by a team from Utah State University.

The researchers, who reported their results in a paper published in the ACS journal Energy & Fuels, examined the properties, engine performance, and emissions for biodiesel produced from the microalgae Chaetoceros gracilis; the yeast Cryptococcus curvatus; and the bacterium Rhodococcus opacus.

While biodiesel derived from plant seed oils has advantages as a replacement for petroleum diesel, there is strong interest in the potential for biodiesel produced from microbial derived oils because of potential use of contaminated water, the diversity of oils that can be produced, use of marginal lands, and potential for higher oil yields per acre. Three different groups of microbes are known to produce high neutral oils including select microalgae, bacteria, and yeast. Here, we have selected a representative from each of these three groups, produced biodiesel, have characterized the properties of the fuels in comparison to biodiesel produced from plant oils.

Plant-based oils, commonly used to produce biodiesel (e.g., soybean, canola, and sunflower) are similar to one another in terms of fatty acid composition, containing primarily C16 and C18 fatty acids with varying degrees of unsaturation. Microbial oils, however, can differ substantially and may contain uncommon fatty acids that differ in both chain length and structure. Each of the microbial sources of oil chosen for this study differ in one way or another from soybean oil, a common feedstock for biodiesel production.

The team determined the key physical properties of each biodiesel and compared them with commercial soybean biodiesel. Each fuel was then used to operate a two-cylinder indirect injection diesel engine attached to an eddy current dynamometer. The horsepower and torque output from the engine under load was reported for each microbial biofuel and compared to outputs obtained with both diesel fuel and soybean biodiesel. Key emissions data were collected for each biofuel without load at a steady 3500 rpm, allowing comparison
to emissions from petroleum diesel and soybean biodiesel.

They found that the selected physical properties of the three microbial fuels were comparable to soybean biodiesel and are within ASTM (ASTM D6751) specification.

In engine testing, diesel #2 delivered the highest power output (8.5 hp) of all fuels. Soybean biodiesel registered a power output of 8.2 hp, 96.5% of the value obtained for diesel #2. Of the microbial fuels tested, bacterial biodiesel had the lowest power output at 7.8 hp, still producing 92% and 95% of the output achieved with diesel #2 and soybean biodiesel, respectively. Power output for the engine operated with both yeast and microalgae biodiesel was similar for each fuel achieving 93% and 96% of outputs for diesel #2 and soybean biodiesel, respectively.>

The team found less of a difference in observed torque output. Exhaust gas temperatures were highest for diesel #2, followed by soybean, microalgae, yeast, and bacteria (in order of decreasing temperatures). The biofuels showed higher fuel consumption (BSFC) across the rpm range of the test compared to diesel #2, which is consistent with their lower energy content. Very small differences in BSFC between the biodiesel fuels were observed.

Hydrocarbon and CO emissions were reduced from diesel #2 levels for all microbial and soybean biodiesel fuels. While NOx emissions are elevated relative to diesel #2 in yeast, bacteria, and soybean biodiesel fuels, microalgae biodiesel fuel generated NOx emissions that were significantly lower, they found. They suggested that the low prevalence of polyunsaturated fatty acids and the predominance of shorter chain length fatty acids present in C. gracilis oil likely contribute to its low NOx emissions.

his study demonstrates that microbial-derived biodiesel shows comparable properties in the parameters tested to soybean biodiesel. Future wide scale use of microbial oils as a source for biodiesel will require advances in large scale cultivation, dewatering, and oil extraction.

Comments

The EGT tracks the power output, suggesting that volumetric fuel delivery was constant and not adjusted for the energy density of each fuel (if reduced power output was a consequence of e.g. slower combustion, EGT would go up).

A true apples-to-apples comparison would equalize the energy delivery of each fuel and see how the outputs differ.

@sd
You can buy a gen-set with an IDI engine at any larger hardware store. It is a cheap and simple way to conduct testing. The study is relevant to – small IDI engines where you do not adjust the injection system to retain power when you switch fuel.

This kind of biodiesel is non-fossil and has a potential to provide a substantial reduction of GHG emissions that LNG/CNG cannot do (LNG/CNG in an otto engine is roughly comparable to diesel fuel in a DI diesel regarding GHG emissions). Likewise, it is much better than current biodiesel, which probably will be “killed” anyway in the EU by the proposed ILUC regulation.

@Peter XX
No one builds a serious contemporary diesel engine with indirect injection. Automotive diesels used to be built with indirect injection because it was quieter but new electronic injection has made it possible to make the engines smoother, quieter, and more efficient with direct injection.

Regarding my comments on LNG/CNG, I was not implying using a spark ignition or Otto cycle. Westport Innovations makes a coaxial direct injection system that injects LNG or CNG along with about 5% diesel for ignition. It is a true diesel and runs with diesel efficiency and the same rated power. It is cheaper and cleaner to run than straight diesel and the LNG infrastructure is currently being built to allow trucks to run cross country using this system. You can go down to your local truck dealer and buy a class 8 truck that uses this system. Also EMD/Caterpillar is currently working on diesel locomotives using this system.

@HarveyD
We will have ICE engines for quite a while. Maybe, you could build an battery driven class 8 long haul truck if they can get lithium air batteries to work and the cost is low enough. Also, you could build an interstate trolley system but I do not expect this in the near term. I would like to see electric locomotives but I expect to see LNG locomotives before we have wide spread electrication.

@sd
Small diesel engines, such as the mentioned gen-sets, are IDI engines even today. Apparently, you did not know that.

If you ever have read my contributions at this site before, you would know that I am perfectly aware about that LNG/CNG can be used in a modified diesel cycle in heavy-duty and large marine engines. However, if we are talking about small engine as this one, or perhaps somewhat larger car engines, there are no LNG/CNG engines using the diesel cycle on the market. I have never seen any information that a car manufacturer is planning to introduce it either. Consequently, on the near term horizon this is not an option at all. Thus, the only option for comparison in a car would be an otto engine using CNG, maybe LNG. Such an engine is no better than a diesel engine regarding efficiency or GHG emissions. In a best case, i.e. in cases (on a specific market) when well-to-tank energy use and emissions are low, LNG/CNG could be marginally better than gasoline. Additional issues are increased weight, limited range and poor performance.

LNG liquefaction and transport use a lot of energy. Much CNG actually also comes via imported LNG, so we have the same problems with waste of energy and increased GHG emissions there. Besides these problems, the simple fact that natural gas is a fossil fuel makes this a dead end. This is particularly valid if we compare on a time horizon when fuels from algae would be ready for the market in large quantities.

BTW, how could you even refer to “near term” in this context? Fuels from algae are on the stage of basic research. I always refer to them as third generation biofuels. Fuels from the second generation are not even commercial yet. On one topic I could agree with you and others. Testing this fuel in an IDI engine makes absolutely no sense. But, of course, it is very, very cheap; you do not even have to invest in a test cell or even a dynamometer. It all comes with the (cheap) gen-set…

I guess what gets me the most is that this soy based fuel is grown on soil that should be producing fuel for human consumption.
Maybe fuel in the gas tank to some is still considered human consumption.
I believe there has to be a better way to produce fuel, without taking food out of children,s mouths. Adults will find a way.
The 50 year old coal fired power plants are being scheduled to be shut down. Can the farm land around these power plants be used to grow this bio diesel feedstock.

Here is another idea. Lets take this 500 to 700 acres of coal infused land, and turn it into algae ponds to produce Bio fuels including diesel fuel.

Now is when you have to let your mind wander.The converted to natural gas power plant has no chimneys. The heat energy is being recovered by the technology of Condensing Flue Gas Heat Recovery.
This recovered heat energy is keeping these algae ponds warm to the growers desired temperature.

The heat energy was recovered from the waste exhaust gases, so what is left is COOL exhaust.
This cool exhaust is cool CO2 and the algae want the CO2. It is fertilizer.
Algae takes in CO2 and gives back OXYGEN, something that makes all of us happy.

And then there is the WATER that is being created during this heat recovery process.
This Clean -Distilled water is very usable.